Autoignition material and method

ABSTRACT

An autoignition material is provided which contains azodicarbonamide (ADCA) serving as a fuel and an oxidizer including at least basic copper nitrate (BCN) as an oxidizing agent for oxidizing the fuel, present in a ratio of ADCA to BCN of at least about 0.5, and a binder, present in a relative amount of no more than 5 weight percent of the autoignition material, serving as a binding agent for binding at least the fuel and the oxidizer, wherein the autoignition material has an equivalence ratio of less than about 0.8.

BACKGROUND OF THE INVENTION

This invention relates generally to autoignition materials suitable for use in inflator devices such as are employed in automotive inflatable restraint systems and, more particularly, to autoignition materials having enhanced aging stability.

Autoignition materials are useful in a variety of different contexts. One significant use for such compositions is in the operation of automotive inflatable restraint systems. It is well know to protect a vehicle occupant using a cushion or bag, e.g., an “airbag cushion” that is inflated or expanded with a gas when a vehicle experiences sudden deceleration, such as in the event of a collision. Such airbag restraint systems normally include: one or more airbag cushions, housed in an uninflated and folded condition to minimize space requirements; one or more crash sensors mounted on or to the frame or body of the vehicle to detect sudden deceleration of the vehicle; an activation system electronically triggered by the crash sensors; and an inflator device that produces or supplies a gas to inflate the airbag cushion. In the event of a sudden deceleration of the vehicle, the crash sensors trigger the activation system which in turn triggers the inflator device which begins to inflate the airbag cushion in a matter of milliseconds.

Typically, such inflator devices include a housing containing one or more gas generant compositions. Such gas generant compositions upon reaction or combustion produce or supply a gas to inflate an associated airbag cushion. In order to inhibit or prevent undesired or premature combustion of the gas generant materials, such gas generant compositions are commonly formulated to have an autoignition temperature which exceeds 180° C. such as, for example, between about 200° C. and about 260° C. When such inflator devices are exposed to abnormally elevated temperatures such as in the event of a fire, however, the inflator device housing may experience excessive thermal stress which can result in a structural weakening of the housing. Thus, upon autoignition of the gas generant materials contained within such an inflator device, pressures generated by the combustion of the gas generant materials can result in rupture and/or fragmentation of the thermally weakened housing. Such rupture and/or fragmentation of the inflator device housing can pose a serious risk of injury to vehicle occupants, rescue personnel or other personnel handling such inflator devices. Moreover, when the gas generant materials contained within an inflator device are exposed to abnormally elevated temperatures, such gas generant compositions may degrade or decompose and become unstable resulting in unpredictable ballistic response upon ignition of the gas generant materials.

One approach to overcoming or eliminating the problems associated with autoignition of such gas generant materials at abnormally elevated temperatures is to provide a material or composition having a lower autoignition temperature, i.e., a material or composition commonly referred to as an “autoignition material” or an “autoignition composition”, within the inflator device. In the event that an inflator device containing such an autoignition material is exposed to abnormally elevated temperatures, the autoignition material will desirably ignite at a temperature lower than that at which undesirable thermal stress of the inflator device housing may occur. Such ignited autoignition material desirably ignites associated gas generant materials at a temperature below that at which undesirable degradation or decomposition of the gas generant materials may occur, i.e., desirably at a temperature between about 145° C. and about 175° C. at a heating rate of about 10° C. per minute.

A variety of autoignition materials or composition have been proposed in the art for inclusion in an inflator device of an automotive inflatable restraint system. Such autoignition materials generally include a fuel and an oxidizing agent or oxidizer in a stoichiometric ratio such that the autoignition material has an equivalence ratio of about 1.0. However, it has been discovered that such stoichiometric autoignition materials while fulfilling the desired autoignition temperature parameters may not age as well as desired. For example, it has been observed that such stoichiometric autoignition materials may be subject to undesirable weight loss and either or both a consequent rise in autoignition temperature and a loss of combustion heat or heat of explosion during aging, such as associated with industry standard aging parameters, e.g., 400 hours at 107° C. or 1000 hours at 90° C. Such aging effects can result in an autoignition material that may not reliably cause the ignition of an associated gas generant material within an automotive inflator device and consequently expose the inflator device and gas generant material to undesirable thermal stresses.

Thus, there is a need and a demand for an autoignition material for use in an automotive inflatable restraint system having enhanced aging characteristics. There is further need and demand for an autoignition material which exhibits reduced weight loss and loss of combustion heat during storage.

SUMMARY OF THE INVENTION

A general object of the invention is to provide an improved autoignition material.

A more specific objective of the invention is to overcome one or more of the problems described above.

The general object of the invention can be attained, at least in part, through an autoignition material including azodicarbonamide fuel and an oxidizer component including basic copper nitrate present in a ratio of azodicarbonamide to basic copper nitrate of greater than about 0.5, and a binder present in a relative amount of no more than about 5 weight percent of the autoignition material; the autoignition material having an equivalence ratio of less than about 0.8.

The prior art generally fails to provide an autoignition material, such as for use in an inflator device of an automotive inflatable restraint system, having enhanced aging characteristics. The prior art further generally fails to provide autoignition materials that are over-fueled, i.e., have an equivalence ratio of less than 0.8, that include azodicarbonamide (ADCA) fuel and basic copper nitrate (BCN) oxidizer in a ratio ADCA to BCN of greater than 0.5, and a relatively small amount of binder, i.e., not more than 5 composition weight percent, such as to reduce or prevent age-induced weight loss, age-induced loss of heat of combustion or explosion and/or age-induced autoignition temperature increases of the autoignition materials.

The invention further comprehends a method of igniting an associated gas generant material including causing an autoignition material to reach an autoignition temperature whereupon the autoignition material ignites the gas generant material at a temperature lower than the autoignition temperature of the gas generant material.

The invention still further comprehends an autoignition material consisting essentially of azodicarbonamide fuel and basic copper nitrate oxidizer present in a ratio of azodicarbonamide to basic copper nitrate of greater than about 0.5, and a binder present in a relative amount of no more than about 5 weight percent of the autoignition material, wherein the autoignition material has an equivalence ratio of less than about 0.8.

As used herein, references to a specific composition, component or material as a “fuel” are to be understood to refer to a chemical that generally lacks sufficient oxygen to bum completely to CO₂, H₂O and N₂.

Correspondingly, references herein to a specific composition, component or material as an “oxidizer” are to be understood to refer to a chemical generally having more than sufficient oxygen to bum completely to CO₂, H₂O and N₂.

As used herein, references to “stoichiometric ratio” or “stoichiometric composition” are to be understood to refer to materials or compositions wherein the fuel to oxidizer ratio is such that all hydrogen in the material or composition is converted to water and all carbon in the material or composition is converted to carbon dioxide. Such stoichiometric compositions have an equivalence ratio of about 1.

References herein to “equivalence ratio” are to be understood to refer to the ratio of the number of moles of oxygen in an autoignition material or composition to the number of moles of oxygen needed to convert all hydrogen to water, all carbon to carbon dioxide, and any metal to the thermodynamically predicted metal oxide. Thus, an autoignition material having an equivalence ratio greater than 1.0 is generally considered over-oxidized, an autoignition material having an equivalence ratio less than 1.0 is generally considered under oxidized, and an autoignition material having an equivalence ratio equal to 1.0 is generally considered stoichiometrically oxidized.

Further, references herein to “over-fueled” or “under-oxidized” compositions or material are to be understood to refer to compositions or materials having an equivalence ratio of less than 0.85 and are lacking sufficient oxygen to completely combust all hydrogen in the composition or material to water and all carbon in the composition or material to carbon dioxide.

Other objects and advantages will be apparent to those skilled in the art from the following detailed description taken in conjunction with the appended claims and drawing.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a simplified cross-sectional view of a gas-supplying inflator device containing an autoignition material.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides improved autoignition materials such as are used in an inflator device in an automotive inflatable restraint system and, more particularly, autoignition materials having enhanced aging characteristics. As described in greater detail below and in accordance with one preferred embodiment of the invention, such autoignition material desirably contains or includes azodicarbonamide (ADCA) serving as a fuel, an oxidizer component including basic copper nitrate (BCN) serving as an oxidizing agent for oxidizing the fuel and a binder serving as a binding agent for binding at least the fuel and the oxidizing agent, wherein the autoignition material has an equivalence ratio of less than about 0.8.

It is generally desirable that autoignition materials for use in automotive inflatable restraint systems meet industry safety standards with regard to aging. However, as discussed above, autoignition materials may over time, become less effective due to loss of weight, reduced heat of combustion and increased autoignition temperatures. In view thereof, there has been an ongoing need for an autoignition material having enhanced aging characteristics. It has now been discovered that by formulating an autoignition material to include azodicarbonamide fuel, an oxidizer including at least basic copper nitrate present in a ratio of ADCA to BCN of greater than 0.5, and a binder present in a relative amount of not more than about 5 composition weight percent of the autoignition material, such that the autoignition material is over-fueled, i.e., has an equivalence ratio of less than 0.8, such autoignition material exhibits enhanced aging characteristics such as, for example, reduced loss of heat of explosion (HEX) and a stable autoignition temperature when compared to a stoichiometric autoignition material.

In accordance with the invention, an autoignition material having an equivalence ratio less than about 0.8 contains azodicarbonamide (ADCA) serving as a fuel, an oxidizer component including basic copper nitrate (BCN) serving as an oxidizing agent for oxidizing the ADCA fuel and a binder serving as a binding agent for binding at least the fuel and the oxidizing agent. In particular, the autoignition material contains azodicarbonamide and basic copper nitrate in a ratio of ADCA to BCN of greater than about 0.5. More particularly, the autoignition material includes azodicarbonamide and basic copper nitrate in a ratio of ADCA to BCN of greater 0.65; suitably in a ratio of ADCA to BCN of greater than about 0.70. In accordance with certain preferred embodiments of the invention, the autoignition material includes the azodicarbonamide fuel in a relative concentration of about 30 to about 50 composition weight percent and the basic copper nitrate oxidizing agent in a relative concentration of about 50 to about 70 composition weight percent.

Further in accordance with the invention, an autoignition material having an equivalence ratio less than about 0.8 includes a binder in a relative amount of no more than about 5 weight percent of the autoignition material. In accordance with certain preferred embodiments of the invention, the autoignition material includes about 2 to about 5 composition weight percent binder and, more particularly, about 2 composition weight percent. Useful binding agents that may be included in the autoignition materials of the invention include any binder known to be compatible with the basic copper nitrate such as, for example, ethyl cellulose, cellulose acetate, hydroxypropyl cellulose, hydroxyethyl cellulose, other substituted celluloses, polyacrylamide and combinations thereof. Selecting a binder that is not compatible with the basic copper nitrate may result in an autoignition material that will decompose at a temperature lower than desired. In accordance with certain preferred embodiments of the invention, the autoignition material includes ethyl cellulose as a binding agent.

In accordance with one preferred embodiment of the invention, an autoignition material having an equivalence ratio of 0.8. consists essentially of azodicarbonamide fuel and basic copper nitrate oxidizer, the fuel and oxidizer present in a ratio of ADCA to BCN of at least about 0.5, and a binder present in an amount of no more than about 5 composition weight percent.

Autoignition materials in accordance with certain preferred embodiments of the invention may desirably further include at least one co-oxidizer such as, for example, a nitrate co-oxidizer. It may be advantageous to include such a nitrate co-oxidizer in the autoignition material in order to stabilize the basic copper nitrate to decomposition during aging. Desirably, such co-oxidizer comprises an alkaline or alkaline earth metal nitrate, a metal amine nitrate complex or combinations thereof. Such co-oxidizer may be included in the autoignition material in a relative concentration of up to about 50 composition weight percent.

In addition, autoignition materials in accordance with the invention may, if desired include one or more additional components or ingredients such as may enhance or provide desirable properties to the autoignition material. For example, metal powders may be included in the autoignition materials in accordance with the invention to increase the heat of reaction of the materials so that an associated gas generant material is more easily ignited by the autoignition materials. Examples of metal powders suitable for use in accordance with the invention include magnesium/aluminum alloys, boron and combinations thereof. In another aspect, autoignition materials in accordance with the invention may desirably include a compound or material that serves as an ammonia scavenger. One such ammonia scavenger suitable for use in accordance with certain preferred embodiments of the invention includes a zeolite such as, for example, chabazite which is also known as acadialite and adipite.

Those skilled in the art and guided by the teachings herein provided will appreciate that suitable autoignition materials in accordance with the invention can be prepared by various methods and the broader practice of the invention is not necessarily limited by or to specific methods of preparation. A preferred method of preparing autoignition materials in accordance with the invention includes the steps of: preparing an ethanol slurry containing at least the azodicarbonamide fuel, the basic copper nitrate oxidizing agent and the binder; drying the slurry; granulating the dried slurry; and pressing the granulated material into tablets. In accordance with certain preferred embodiments of the invention, the autoignition material tablets may be placed or loaded into an inflator device.

Referring to the FIGURE, an inflator device 20 includes an housing 22 having a first end 24 and a second end 26 opposite the first end 24. The housing 22 shown in the FIGURE is generally tubular in shape and an inner surface 28 of the housing 22 defines a storage chamber 30. A supply of gas generant material 32 is disposed within the storage chamber 30. The supply of gas generant material 32 desirably includes a plurality of gas generant material bodies having a form selected from a group consisting of tablets, wafers, extrudlets and combinations thereof.

In accordance with certain preferred embodiments of the invention, a supply of an autoignition material 34 is interspersed with the gas generant material 32 within the storage chamber 30. The supply of autoignition material 34 desirably includes a plurality of autoignition material bodies having a form selected from a group consisting of tablets, wafers, extrudlets and combinations thereof. Desirably, the supply of autoignition material 34 is in actuating communication with at least a portion of the supply of gas generant material such that in the event of exposure to abnormally elevated temperatures, i.e., in the event of a fire, the supply of autoignition material 34 is able to actuate or initiate reaction of at least a portion of the supply of gas generant material 32. In one embodiment of the invention, as shown in the FIGURE, the supply of gas generant material 32 and autoignition material 34 is more particularly contained in a generant cannister 36, having an inner surface 38, disposed within the storage chamber 30.

An initiator assembly 40 is joined to the housing first end 24. The initiator assembly includes an initiator 42 having a pair of electrical conductive pins 44 oriented toward the housing first end 24. The initiator assembly 40 is joined to the housing 22 such that the initiator 42 is disposed in actuating communication with at least a portion of the supply of gas generant material 32. In other words, the initiator is joined to the housing 22 such that, upon receiving an electrical charge signal, the initiator 42 is able to actuate or initiate reaction of at least a portion of the supply of gas generant material 32.

As will be appreciated by one skilled in the art following the teachings herein provided, the size, shape, construction and configuration of an inflator device in accordance with the invention can be appropriately varied dependent on factors such as the configuration and desired performance of the inflator device and the broader practice of the invention is not necessarily limited to or by the specific inflator device depicted in the FIGURE.

Those skilled in the art and guided by the teachings herein provided will appreciate that a variety of gas generant materials may be ignited by suitable autoignition materials in accordance with the invention by various methods and the broader practice of the invention is not necessarily limited to or by specific methods of use. A preferred method of igniting a gas generant material includes the steps of: causing an autoignition material to reach an autoignition temperature whereupon the autoignition material ignites an associated gas generant material. In accordance with certain preferred embodiments of the invention, the autoignition temperature is in a range of about 145° C. and about 175° C.

The present invention is described in further detail in connection with the following examples which illustrate or simulate various aspects involved in the practice of the invention. It is to be understood that all changes that come within the spirit of the invention are desired to be protected and thus the invention is not to be construed as limited by these examples.

EXAMPLES

Autoignition materials were prepared having the compositions identified in TABLE 1 below. The autoignition materials in accordance with Comparative Example 1 (CE1) and Comparative Example 2 (CE2) each had an equivalence ratio (ER) of about 1.0 while the autoignition material of Example 1 (EX1), in accordance with the invention, was over-fueled, i.e., had an equivalence ratio of less than 0.8. TABLE 1 CE1 CE2 EX1 Ethyl Cellulose 2.00 4.00 2.00 ADCA 28.34 23.21 40.00 BCN 64.66 67.79 53.00 Chabazite 5.00 5.00 5.00 ER 1.00 1.00 0.78 ADCA/BCN ratio 0.44 0.34 0.75 ADCA = Azodicarbonamide BCN = Basic copper nitrate Test Methods and Data:

Samples of each of the autoignition materials were tested to determine the Autoignition Temperature (AIT), measured at heating rate of 10° C./minute, before aging, after aging at 107° C. for 400 hours and after aging at 90° C. for 1000 hours. The autoignition temperatures were measured by placing samples of each material to be tested in a test tube held in an aluminum block equipped with a temperature sensor. The aluminum block holding the test tubes was placed in a furnace equipped with a variable rate temperature controller. The samples were heated at a heating rate of 10° C./minute until the samples were observed to autoignite, i.e., the samples were heated to the temperature at which the production of light and heat were observed. The results of the AIT testing appears in TABLE 2 below.

Samples of each of the autoignition materials were also tested to determine the heat of explosion (HEX) before and after aging. Samples of each material to be tested were placed in a Parr apparatus equipped with temperature sensors and ignited. The amount of heat liberated by the ignition of the test materials was recorded and appears in TABLE 2 below.

Samples of each autoignition material were further tested to determine the percentage weight loss after aging. Samples of each autoignition material to be tested were weighed and placed into containers. The containers were placed in an oven at a pre-set fixed temperature, i.e., 107° C. and/or 90° C. The samples were held or aged at the fixed temperature for a fixed period of time, i.e., 400 hours or 1000 hours. After aging the samples were weighed and the percentage weight loss was calculated by dividing the difference between the weight of the sample before aging and after aging by the weight of the sample before aging. The results of the weight loss testing appear in TABLE 2 below. TABLE 2 CE1 CE2 EX1 AIT 165 162 163 AIT 107° C. Aging 171 174 162 AIT 90° C. Aging 162 166 160 HEX 396 385 428 HEX 107° C. Aging 298 306 368 HEX 90° C. Aging — — 417 Wt. Loss 107° C. Aging 17.30% 17.89% 17.90% Wt. Loss 90° C. Aging  4.80%  5.60%  9.40% Discussion of Results

While the autoignition materials of each of Comparative Example 1, Comparative Example 2 and Example 1 experienced a loss of weight and a reduction in heat of explosion during aging, the over-fueled autoignition material of Example 1 and in accordance with the invention demonstrated relatively less change in autoignition temperature (AIT) and heat of explosion (HEX) when compared to the stoichiometric autoignition materials in accordance with Comparative Example 1 and Comparative Example 2 as shown in TABLE 2 above.

Thus, the invention provides an improved autoignition material suitable for use in an automotive inflatable restraint system inflator device, and, more particularly, an autoignition material having enhanced aging characteristics.

The invention illustratively disclosed herein suitably may be practiced in the absence of any element, part, step, component, or ingredient which is not specifically disclosed herein.

While in the foregoing detailed description this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purposes of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention. 

1. An autoignition material comprising: azodicarbonamide serving as a fuel; an oxidizer component comprising basic copper nitrate and serving as an oxidizing agent for oxidizing the fuel, the azodicarbonamide and basic copper nitrate present in a ratio of azodicarbonamide to basic copper nitrate of greater than about 0.5; and a binder serving as a binding agent for binding at least the fuel and the oxidizing agent, the binder present in a relative amount of no more than about 5 weight percent of the autoignition material; wherein the autoignition material has an equivalence ratio of less than about 0.8.
 2. The autoignition material of claim 1 wherein the azodicarbonamide and basic copper nitrate are present in a ratio of azodicarbonamide to basic copper nitrate of greater than about 0.65.
 3. The autoignition material of claim 1 wherein the azodicarbonamide and basic copper nitrate are present in a ratio of azodicarbonamide to basic copper nitrate of greater than about 0.70.
 4. The autoignition material of claim 1 wherein the azodicarbonamide is present in a relative amount of about 30 to about 50 composition weight percent.
 5. The autoignition material of claim 1 wherein the basic copper nitrate is present in a relative amount of about 50 to about 70 composition weight percent.
 6. The autoignition material of claim 1 wherein the oxidizer component additionally comprises at least one co-oxidizer.
 7. The autoignition material of claim 1 wherein the oxidizer component additionally comprises at least one co-oxidizer selected from the group consisting of at least one alkaline metal nitrate, at least one alkaline earth metal nitrate and at least one metal ammine nitrate complex.
 8. The autoignition material of claim 1 wherein the binder comprises ethyl cellulose.
 9. The autoignition material of claim 1 wherein the autoignition material consists essentially of azodicarbonamide, basic copper nitrate and a binder.
 10. A gas-supplying inflator device comprising the autoignition material of claim
 1. 11. In the gas-supplying inflator device of claim 10 wherein the gas supplying inflator device additionally comprises a quantity of gas generant material, a method of igniting the gas generant material, the method comprising: causing the autoignition material to reach an autoignition temperature whereupon the autoignition material ignites the gas generant material.
 12. The method of claim 11 wherein the autoignition temperature is in a range of about 145° C. to about 175°.
 13. An autoignition material consisting essentially of: azodicarbonamide serving as a fuel; basic copper nitrate serving as an oxidizing agent for oxidizing the fuel, the azodicarbonamide and basic copper nitrate present in a ratio of azodicarbonamide to basic copper nitrate of greater than about 0.5; and a binder serving as a binding agent for binding the azodicarbonamide and basic copper nitrate, the binder present in a relative amount of no more than about 5 weight percent of the autoignition material; wherein, the autoignition material has an equivalence ratio of less than about 0.8.
 14. The autoignition material of claim 13 wherein the binder comprises ethyl cellulose.
 15. A gas-supplying inflator device containing the autoignition material of claim
 13. 16. In the gas-supplying inflator device of claim 15 wherein the gas supplying inflator device additionally contains a quantity of gas generant material, a method of igniting the gas generant material, the method comprising: causing the autoignition material to reach an autoignition temperature whereupon the autoignition material ignites the gas generant material.
 17. The method of claim 16 wherein the autoignition temperature is in a range of about 145° to about 175° C. 